The designer of an output stage for a CMOS integrated circuit frequently chooses circuit parameters and device geometries that reflect the most pessimistic combination of manufacturing process variations and operating temperatures that are likely to be encountered. In systems that operate at high speeds and with low values of VDD, it is common for output stages to drive transmission lines that are capacitively terminated to produce a doubling of voltage. This scheme requires that the output impedance of the driver match the characteristic impedance of the transmission line, both when it is pulling up to VDD and pulling down to GND or to Dirty GND (DGND). If it does not, then possible undesirable side effects include increased rise times, overshoot and ringing. Overvoltage conditions and excessive power dissipation in the pull down device are possible associated outcomes, not to mention reduced density for the IC owing to the fabrication of devices larger than would otherwise be necessary. Unfortunately, however, the variations in IC manufacturing processes and in ambient operating temperature can combine to produce changes in output driver stage output impedance that can be several-fold to one. This situation limits system performance and increases costs. It would be desirable if the output impedance of a CMOS output driver stage could be externally programmed over a wide range of values after the IC was manufactured, irrespective of any variations in the processing parameters that produced the IC. It would be further desirable if would-be variations in the output impedance arising from changes in temperature were automatically compensated. Lastly, it should not be necessary to experiment with any particular IC to determine what programming value to use to produce the desired output impedance. Any IC of a particular type should program to that desired output impedance with a programming value known in advance, regardless of any manufacturing process variations that may be associated with specific individual IC's of that particular type.